The present invention relates generally to ceiling dampers, and in particular, relates to a ceiling damper having an improved fusible link assembly and pivot arm geometry to produce enhanced strength characteristics.
Building and fire codes require that fire dampers be placed in specified heating, ventilation, and air conditioning ducts. Dampers operate in a normally open position, which allows air to flow through the ductwork, and close in response to a predetermined stimulus, such as a dramatic increase in temperature, indicating a fire or other hazardous condition. In particular, conventional dampers include a pair of damper blades that are held open by a fusible link. When the fusible link fails in a predetermined manner in response to the elevation in temperature, the mechanical interference maintaining the blades in their open position is removed, thereby permitting the damper to close and form a seal with the duct. As a result, air is prevented from circulating throughout the building in response to a fire or other hazardous condition.
One such conventional damper assembly, described in U.S. Pat. No. 4,366,830, includes a pair of damper blades that are joined together by a hinge member that allows the blades to close under the biasing force of a spring member. A pair of damper arms support the blades in their open position against the spring force, and are pivotally connected to the side walls of a mounting bracket. In particular, the terminal ends of the damper arms are inserted in to apertures extending through the side walls at a pivot location. A flat retainer plate is mechanically connected to the outer surface of the base of the mounting bracket via an axially extending screw. The retainer plate is further soldered to the upper surface of the base of an outer housing. The outer housing encases the mounting bracket and includes a pair of side walls that support the damper arms at a support location. When the solder melts in response to an elevation in temperature, the bracket and damper arms translate axially upwardly with respect to the housing, thereby removing the housing from interference with the damper arms. The damper arms therefore close under the basing spring force, which correspondingly closes the damper blades.
This design incorporates strength deficiencies in several respects. To begin, the distance between the pivot point and the support location as measured in the axial direction is no greater than xe2x85x9c inch. A significant force is thereby imparted onto the damper arms, which may fail prematurely as a result. Accordingly, the blades may close in an unreliable manner during normal operation. Additionally, because the arms are supported by the outer housing, which is soldered to the retainer plate, the force imparted onto the damper arms is transferred to the housing, and thus to the retainer plate. Testing has indicated that the retainer plate may warp due to the resulting stresses experienced during normal operation. This may crack the solder joint, and cause the damper assembly to fail prematurely.
What is therefore needed is a damper assembly having improved strength characteristics to minimize the stress experienced by the pivot arms as well as the support members so as to prevent the damper from closing prematurely.
The present invention recognizes that conventional ceiling dampers may be modified to enhance their strength characteristics, thereby minimizing the risk of premature failure.
In accordance with one aspect of the invention, a damper assembly is disclosed having at least one damper blade operating between an open and closed position to control fluid flow through a conduit. The damper assembly comprises a bracket defining a base and a first and second oppositely disposed side walls extending upwardly therefrom. A damper arm supports the at least one damper blade and has terminal ends connected to the side walls at a pivot location to permit the arm to rotate between an open and a closed position. A fusible link assembly is coupled to the bracket and includes a housing member defining a support structure that engages the damper arm at a support location and interferes with the rotation of the damper arm, and a channel member removably fused to the housing member via a fusible link. The channel member includes a base and first and second side walls extending upwardly therefrom, wherein the channel member separates from the housing member when the fusible link reaches a predetermined temperature. The interference between the support location and the damper arm is removed when the channel member separates from the housing member to allow the damper arm to pivot about the pivot location and close the at least one damper blade.
In accordance with another aspect of the invention, the pivot location and support location define an axial distance therebetween of greater than xe2x85x9c inch.
This and other aspects of the invention are not intended to define the scope of the invention for which purpose claims are provided. In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, and not limitation, a preferred embodiment of the invention. Such embodiment also does not define the scope of the invention and reference must therefore be made to the claims for this purpose.